Small molecule probes are powerful tools for studying biological systems and can also serve as lead compounds for developing new drugs to treat human diseases. To enable the identification of such probes, the overall objective of this project is to synthesize novel small molecule libraries for submission to the NIH Molecular Libraries Small Molecule Repository (MLSMR) and screening against a wide range of biological targets in the Molecular Libraries Probe Production Centers Network (MLPCN). To date, pharmaceutical companies and, hence, commercial library suppliers, have largely focused on a small set of ~200 'druggable' biological targets and, as a result, increasingly narrow regions of chemical structure space that correlate with these targets. Sequencing of the human genome has opened the door to using small molecules to investigate a vast array of exciting new targets. However, existing libraries of 'drug-like' molecules often fail to provide useful probes for these targets. Thus, to address this broader range of biological targets through screening in the MLPCN, a wider variety of chemical structures must also be represented in the MLSMR. To meet this need, we propose to continue our comprehensive program to synthesize pilot-scale libraries based on specific, privileged substructures from biologically active natural products. These libraries access biologically relevant regions of chemical space that are currently underrepresented in the MLSMR. Stereoselective syntheses are used to provide libraries with diverse three-dimensional scaffolds that are further diversified using building block-coupling reactions. The libraries are designed to afford lead-like properties, aqueous solubility, chemical stability, and cell permeability and will address specific hypotheses regarding the utility of natural product-based pharmacophores, the relative impacts of scaffolds and building blocks, and biased building block sets. The specific aims of this project are to synthesize pilot-scale libraries in the following four classes: (1) aliphatic and benzannulated spiroketals, (2) complex polyketides and peptide-polyketide hybrids, (3) macrolides and related macrocycles, (4) polycyclic alkaloid/terpenoid-like molecules. PUBLIC HEALTH RELEVANCE: The overall goal of this project is to produce novel collections of molecules that resemble biologically active natural products. These libraries will then be tested to identify new probes to study fundamental biological processes and to evaluate new potential therapeutic targets for the treatment of human diseases.